Process for producing and developing light-sensitive photographic layers



Patented Sept. 21 1954 PROCESS 'FOR PRODUCING AND DEVELOP- INGLIGHT-SENSITIVE PHOTOGRAPHIC LAYERS Carlo Rossi, Basel, Switzerland,assignor to Ciba Limited, Basel, Switzerland,.a Swiss firm No Drawing.Application April 2, 1951,

Serial No. 218,893

Claims priority, application Switzerland April 6, 1950 4 Claims.

For some purposes it is necessary to produce substantially grainlessphotographic or lightsensitive layers or films, and for this purpose ithas been proposed to sensitise a substantially grainless water-absorbentlayer or film which is itself not sensitive to light or is quiteinsufficiently sensitive, for example, a gelatine layer, for recordingan image. This problem arises, for example, in connection with layers orfilms which have a grating, especially in connection with U. S.application Serial No. 145,661 of February 23, 1950, which describes themanufacture of lenticular films having a high degree of light activity,

and of which a special characteristic is the use,

of a support having a grating on both sides. For recording an imagephoto-active systems are proposed which consist of light-sensitive diazocompounds and silver or mercury salts (Kalle German Patent No. 640,233and Philips Techn. Rundschau, Jahrgang 9, Nos. 3 and 10, pages 65-96 and289-320).

The aforesaid sensitising solutions made with light-sensitive diazocompounds are known to have the disadvantage of a relatively highinstability, so that it is necessary for copying purposes to expose anddevelop the sensitised material immediately after it has been dried.

The decomposition of the diazo solutions used leads to the formation ofphenol derivatives having a reducing action, and these derivatives causeundesired fogging especially in colloid layers, when an intensifyingdevelopment by means of unstable noble metal baths is used.

Sensitising solutions such as are described, for example, in GermanPatent No. 707,461, deposit considerable amounts of solid decompositionproducts in the course of 24 hours at room temperature and are thereforediflicult to use in a copying establishment.

The present invention is based on the observation that substantiallygrainless water-absorbent layers or films for recording images can besensitised by treating them with a solution of acid reaction whichcontains a complex iron salt and a silver salt.

It is obviously necessary that the waterabsorbent-layers or films usedasstarting materials in the present process should be sufficiently inerttowards the Sensitising solution and especially should contain nosubstances which themselves reduce silver salts or prevent such areduction taking place owing to their oxidising action. Moreover theselayers or films must be substantially grainless. Thus, there may be usedas starting materials substantially grainlesshydro- 2 philic colloidmaterials such as cellulose hydrate films or layers, for example, filmswhich consist wholly of regenerated cellulose or films which consist ofcellulose esters, such as cellulose acetate or mixed esters, such ascellulose acetate butyrate, which have been partially hydrolyzed, butpreferably gelatine layers, and which films or layers may as statedabove have a special form, for example, a lenticular grating, forproducing special effects. The solutions used for sensitising in thepresent process may contain as a complex iron salt, especially a complexferric salt, for example, a complex salt of an inorganic acid such asferric ammonium sulphate, but especially complex salts of organiccarboxylic acids, which may be mono-, di-, or polycarboxylic acids,which advantageously contain one or more hydroxyl groups. The iron boundin complex union may be present in an anion or a cation. As examplesthere may be mentioned hexaaceto-hydroxo-triferric acetate nitrate,ferric ammonium oxalate, potassium diglycollato-ferrate, sodiumdilactato ferrate, potassium disalicylato-ferrate and especially ferriccomplex compounds which contain as the organic carboxylic acid citricacid for example, the brown and especially the green ferric ammoniumcitrate.

While certain of these complex compounds themselves exhibit an acidreaction, it may in other cases be necessary or advantageous in order toimpart the acid reaction to the aforesaid sensitising solutions to add afree acid, for example, nitric acid, glycollic acid or citric acid.

In many cases it is also advantageous to add dyestuffs to thesensitising solutions described above. By the addition of suitabledyestuffs it is possible, for example, to increase the absorption oflight in a desired region of the spectrum. Moreover, it is desirable inmany cases to restrict the depth of penetration of the latent image intothe water-absorbent layer or film, for example, in order to impart avery high resolving power to the light-sensitive layer or film, or, inthe case of the above-mentioned double grating films, to reduce or avoidthe danger of deformation of the lenticulations. For these purposes itis of advantage to add suitable dyestuffs, which then act as dampingdyestuffs.

The aforesaid damping dyestuffs, in addition to possessingthe desiredoptical properties, must sufliciently fulfil the condition of notleading to reactions with the other components of the sensitisingsolution, which reactions would adversely ,affect the presentphoto-chemical system, and depending on the purpose in view they must be3 easily removable. As damping dyestuffs there are suitable for exampletartrazine or a pyrazclone dyestuif of the constitutional formula Theaforesaid acid-reacting solutions, which contain a complex iron salt ofan organic carboxylic acid and a silver salt, usually produceprecipitates shortly after they have been prepared or mixed, and theseprecipitates are harmful in the production of light-sensitive layers orfilms. It has been unexpectedly found that by clarifying the solution,for example, by filtering, decanting or centrifuging, stable solutionsare obtained which when stored at room temperature in the dark for a fewweeks remain unchanged without any appreciable alteration in theircomposition. In the present invention, therefore it is of advan tage tostart with solutions which have been subjected to a clarifying operationafter standing for a short time.

The treatment of the water-absorbent layers or films with the aforesaidsolutions may be carried out in a manner in itself known, for example,by immersion or impregnation by means of a roller or in anyother'manner, so that the waterabsorbent layer or film is uniformlyimpregnated with the solution. The resulting layers or films areconsiderably more stable than the hitherto known layers or filmsproduced with diazo compounds and can be stored, for example, forpcriods ranging from several days to weeks before they need be used.

The new photographic layers of films possess a resolving power (about1000 lines per mm.) similar to that of layers or films prepared withmetal diazo compounds. When used for copying they yield pale yellow topale brown images.

The invention is also based on the observation that these images. can bedeveloped to neutral grey to black tints of good covering'power bydevelopment with unstable noble metal solutions, for example, solutionswhich contain in addition to a silver salt, especially silver nitrate, aphotographic developing substance, such as Metol, and also a weak acidfor example tartaric acid. Unexpectedly development takes place withremarkable freedom from fog, especially in the case of light-sensitivelayers or films which have not been stored for long periods, forexample, for not more than 1-2 weeks.

The aforesaid intensifying development (see Eder, Rezepte, Tabellen undArbeitsvorschriften fiir Photokopie und Reproduktionstechnik, page 80,1927) by means of unstable noble metal solutions is advantageouslycarried out by means of silver nitrate and a reducing component, such asferrous sulphate, hydroquinone or parahydroxymethyl aniline, in an acidmedium. As is generally known from the early literature of the collodiontechnique the silver nitrate may be used either in admixture with thereduction component or before or after the action of the componentprecipitating the silver. It is also possible, for example, toincorporate the silver nitrate necessary for development in thephoto-sensitive layer or film,'so that for the purpose of development itis necessary to treat the exposed layer-or film only with'the reducingcomponent. 'It'may often also be of advantage first to bring theex- 4posed layer or film into contact only with wateror slightly acidulatedWater, and intensify the resulting yellow image by one-of the variantsmentioned above to produce a useful image.

It is of advantage finally to wash the developed film well withdistilled water, which may be carried out at room temperature or aslightly raised temperature depending on the degree of hardness of thecolloid layer.

Images developed in the manner described above generally have a valuableneutral grey to black tint. Depending on the nature of the solution usedfor sensitisation the image may possess more or less pronouncedhalf-tones. For certain copying purposes it is known to be important toobtain records which are practically free from half tones, and thiscondition can be fulfilled to a great extent in the present process.Furthermore it is possible that slight brownish borders may be presentbetween the covered and uncovered parts in the record.

These borders which owing to their brownish tint are in some casesundesirable can be made to disappear, that is to say they can beconverted to neutral grey or black, by treating the developed recordwith a solution of a'metal salt of which the metal is more noble in theelectromotive series than the metal which was used for development. Asexamples of such metal salts there may be mentioned the complexcompounds of hydrohalic acids with noble metals such as gold andplatinum, especially chloroplatinic acid.

The following examples illustrate the invention, the parts andpercentages-being by weight unless otherwise stated and the relationshipofipartsby weight to parts by volume being the sam'e as that of the gramto the cubic centimetre:

Example-1 A layer consisting of light-tanned gelatine, for example, adouble lenticular film made by the process of Dr. Gretener A. G.,Zurich, is impregnated with a sensitising solution, which has beenclarified by filtration after about 4 hours, of the followingcomposition:

parts'of "distilled water,

10 parts of hexa-a'ceto hydrox'o triferric acetate nitrate,

5 parts of silver nitrate,

0.2 part of a non-ion'active wetting agent con-- sisting of thecondensation product of higher fatty alcohols with about 20"molecularproportions of ethylene oxide.

The wet film is driedin a dust-free-current of air heated at 33-35 C.,.and is then used for copying.

The exposed film is developed by .immersi'ng it in a freshlypreparedmixture of iO sparts by volume of an aqueous solution consistingof.

4 per cent. of tartaricacid,

2 per cent. of Metol'and 0.2 per cent. of a non-ion active wetting agentof the type described above and- 2 parts, by volume of a silver nitratesolution-of 10 per cent. strength.

' The development is 1 complete in 4-5 Jmin'utes at 20-21 C. and'thefilm may be dried a'f-terithas been washed in distilled water.

Example "2' Instead of the :sol'u tionv used. in Example 1,

110 parts of distilled water,

10 parts of ferric ammonium oxalate, 1 part of silver nitrate,

20 parts by volume of 2 N-nitric acid.

Before use the above solution is filtered to remove constituents whichhave precipiated.

Alternatively there may also be used instead of the solution mentionedin Example 1, a solution prepared as follows:

In parts of distilled water containing 0.2 per cent. of a wetting agentdescribed in Example 1 are dissolved 0.2 part of potassiumdiglycollatoferrate and 0.1 part of glycollic acid. The clear solutionis mixed with 5 parts of a silver nitrate solution of per cent.strength, and then freed from small quantities of insoluble matter byfiltration.

Finally, there may also be used a solution prepared as follows:

1 part of a solution of 22.4 per cent. strength of green ferric ammoniumcitrate in distilled water is mixed with '1 part by volume of a. silvercitrate solution of 10 per cent. strength.

In all the above cases the development may be carried out in the mannerdescribed in the third and fourth paragraphs of Example 1.

Ercample 3 A sensitising solution is prepared as follows:

52 parts of brown ferric axmnonium citrate and 18.4 parts of citric acidare dissolved together in 200 parts of distilled water. Afterdissolution 5 parts of an aqueous solution of '15 per cent. strength ofa non-ion active wetting agent and 200 parts of a silver nitratesolution of 10 per cent. strength are added.

During mixing a small quantity of a colloidal precipitate separates,which is removed from the solution before use by centrifuging.

The resulting solution is used for impregnating the hardened gelatineside of a double grating film and the resulting film is dried at 33-36C. in dust-free air.

The sensitising solution described above, during storage in the dark atroom temperature precipitates only a trace of a dark coloured deposit inthe course of the first few days, but, if it is then filtered, itremains absolutely clear for 14 days and facilitates the production ofreproducible products.

The layers obtained in accordance with the foregoing examples can bestored in the dark for a long time, for example for a month at a roomtemperature of 18-20" C. without any crystalline deposits or chemicaldecomposition reactions being observed. It is important to maintainprotective drying conditions and to store the products in a dry state.

Example 4 By this treatment the coloured borders are con- 75 e? I vertedinto neutral grey to black parts of the image.

Example5 26 parts of brown ferric ammonium citrate, 9.2 parts of citricacid, 8.0 parts of the salt-free azo dyestuff obtained by coupling1-(2::5-disulphophenyl)-3-methyl-5-pyrazolone with diazotizedsulphanilic acid with the addition of pyridine; and 1.0 part of anon-ionic wetting agent of the type of a fatty alcohol-polyethyleneoxide condensation product are dissolved in 100 parts of distilledwater.

To the resulting mixture is added a solution of 10 parts of silvernitrate in 100 parts of distilled water, and the reaction mixture, fromwhich an amorphous precipitate then separates, is stored at roomtemperature.

Before use the stored sensitising solution'is freed from the originalprecipitate and from the deposit subsequently formed during standing bycentrifuging.

The sensitising solution so obtained can be used instead of thatdescribed in Eample 1, 2 or 3.

Example 6 A cellulose acetate butyrate film, which is provided with acylinder grating, is hydrolysed on its smooth surface about 4 deep withan alcoholic solution of caustic soda by placing it for 4 minutes on thesurface of the hydrolysing solution.

For preparing the hydrolysing solution 16 grams of sodium hydroxide aredissolved in cc. of distilled water, and the whole is made up to 100 cc.by the addition of alcohol of 96 per cent. strength. The solution isclarified by filtration and then used immediately.

After the hydrolysis, the film is freed from excess of caustic soda bywashing in distilled water for 10 minutes and dried in the air. It issensitised with the solution described in Example 3 by immersion forabout 1 minute and washing the side of the film carrying the gratingwith distilled water.

The sensitised film is dried at 33-34 C. for 10-20 minutes by passingdust-free air over it.

In order to obtain favourable or constant copying values, and also toincrease the threshold sensitivity, the exposed film is conditioned,before development, in a room having a temperature of 20-22 C. and arelative humidity of 90-95 per cent. for A hour.

The same conditioning treatment may be applied to the layers used inExamples 1, 2, 3 and 5. Generally speaking, an atmosphere of high watercontent, such as above per cent. relative humidity and preferably aboutto per cent. relative humidity should be used.

What is claimed is:

1. A process for producing photographic records, which comprisesimpregnating a substantially grainless hydrophilic colloid layersupported by a substantially grainless transparent film material, with aclarified acidulated solution which contains a complex ferric salt of analiphatic hydroxy-carboxylic acid and a water soluble silver salt,exposing the sensitized layer and developing it with a solution ofMetol, a weak acid, silver nitrate and a non-ionic wetting agent.

2.. A process for producing photographic records, which comprisessensitizing a substantially grainless hydrophilic colloid layer on atransparent grainless film support with a clarified solution containinghexa acto-hydroxo-triferric ace- '1 tate nitrate, silver nitrate and; anon-ionic. wet.- ting agent, exposing the sensitized layer and (13-veloping it with a solution of Metol, tartaric acid, silver nitrate anda non-ionic. wetting agent.

3. A process as in claim 2 wherein. the sensitized layer is conditionedafter exposure and before development in an atmosphere of at. least 60%relative humidity.

4. A process as in claim 2 wherein the sensitizing solution contains. asilver latent image sensitizing. dye which restricts the depth of.penetration of said latent image into said hydrophilic layer.

References Cited in the file of this patent UNITED STATES PATENTS NumberNumber Namev Date. 1,225,146 Leighton et at. -May 8, 19.17- 1,396,592Rheinberg Nov. 8, 1921 1,984,471 Fischer; Dec. 18, 1934 FOREIGN PATENTSNumber Country Date 5,374 GreatBritain Feb. 15, 1890 375,849 GreatBritain June 30, 1932 439,241 Great Britain Nov. 26,, 1935 538,245 GreatBritain July 25, 1941 OTHER REFERENCES Wall; Intensification andReduction (1927),,

American PhotrP'ub. Co., Boston, Mass pp; 11, 12 and 14.

Neblette: Photography Principles andPractice,v

4th ed. (1942),, pub. by Van Nostrand Co., Inc., New York city,. pages701-703.

1. A PROCESS FOR PRODUCING PHOTOGRAPHIC RECORDS, WHICH COMPRISESIMPREGNATING A SUBSTANTIALLY GRAINLESS HYDROPHILIC COLLOID LAYERSUPPORTED BY A SUBSTANTIALLY GRAINLESS TRANSPARENT FILM MATERIAL, WITH ACLARIFIED ACIDULATED SOLUTION WHICH CONTAINS A COMPLEX FERRIC SALT OF ANALIPHATIC HYDROXY-CARBOXYLIC ACID AND A WATER SOLUBLE SILVER SALT,EXPOSING THE SENSITIZED LAYER AND DEVELOPING IT WITH A SOLUTION OFMETOL, A WEAK ACID, SILVER NITRATE AND A NON-IONIC WETTING AGENT.